The interrelationships between central respiratory drive, and apnea triggered by the laryngeal chemoreflex, will be studied in newborn and young piglets. We have previously shown that acute hemodilutional anemia and chronic spontaneous anemia increase the sensitivity of the young piglet to respiratory depression with chloralose. This effectively enhances the potency of the laryngeal inhibitory reflex. Attempts to produce iron deficiency anemia have been partially successful, and in all incidences associated with varying degrees of growth retardation. We plan to proceed with a model for chronic hemolytic anemia by giving weekly injections of phenyl hydrazine (40 milligrams/kg, i.p.) per week. It is anticipated that this will yield a more predictable chronic anemia, and may not be associated with growth retardation. Piglets from 2 weeks to 3 months of age will be studied under conditions of "pharmacologic sleep." They will be anesthesized with precisely 25 milligrams/kg of sodium pentobarbital, and arterial and venous catheters will be placed. Dual tracheal cannulation will be performed. Central respiratory drive will be assessed by the sequential addition of chloralose (6 milligrams/kg) at 2 minute intervals. The relative gain of the laryngeal reflex will be assessed by the addition of water and milk into the laryngeal area through the superior tracheal catheter. The effects of these manuevers will be quantified by changes in respiratory rate, and by appearance of sustained apnea. Arterial pressure and heart rate, and blood gases, pH and hematocrit will be measured at appropriate intervals. The contribution of adrenergic mechanisms will be assessed in additional piglets pretreated with reserpine (1 milligram/kg) 2 to 3 days prior to study. The effectiveness of this agent in diminishing tissue catecholamines will be determined from brain tissue samples in selected preparations. The appearance of sustained apnea during laryngeal stimulation with water or milk, and the lethal dose of chloralose will be assessed in these preparations, and compared with age-matched animals in the anemic and control groups. BIBLIOGRAPHIC REFERENCES: Lee, J.C., B.J. Stoll and S.E. Downing. Properties of the laryngeal chemoreflex in neonatal piglets. Am. J. Physiol. 232: 1977, In Press.